Date   : Thu, 16 Jul 2009 20:46:56 +0100
From   : philb@... (Phil Blundell)
Subject: happy bunny

On Thu, 2009-07-16 at 13:08 -0500, Jules Richardson wrote:
> Rob wrote:
> > Eek some horror stories there.  Best I can manage is a full-height
> > ST506 type drive that would only read data if positioned upside down.
> 
> Yeah, I've had that before. Plus with at least some st506/412 drives you were 
> supposed to re-do the low-level format if you changed their orientation (I 
> think later ones were better in that regard)

That tended to happen with the old, big ones that did their head
positioning by dead reckoning (floppy-style: seek to track zero, move
out by so many steps, and hope for the best).  The head mechanisms were
big and heavy enough that, if you mounted the disk on its side, gravity
would tend to pull the head further towards one side or the other.  If
you then turned the drive around, all of a sudden the head would drift
in the other direction and it wouldn't line up with the tracks anymore.

With 3.5" disks this problem didn't seem to happen so much, presumably
because the mechanisms were smaller.  On modern "voice coil" drives it
isn't an issue at all because they use a servo mechanism to line the
head up with the track rather than just blindly positioning it in what
they hope is the right place.

p.